Heart disease remains the largest major cause of death of both men and women in the U.S. According to the latest report on Heart Disease and Stroke Statistics, more than 2200 Americans die of cardiovascular disease (CVD) each day, an average of 1 death every 39 seconds. Arrhythmias refer to the disruption of the natural heart rhythm. This irregular heart rhythm causes the heart to suddenly stop pumping blood. Atrial pathologies are the most common arrhythmias with atrial fibrillation and atrial flutter being the most prevalent and powerful risk factors for stroke with a 5-fold increase throughout all ages and an associated cost of $6.65 billion per year in treatment. Despite this urgent clinical need, t date there is simply no imaging modality available in the clinic that can noninvasively map the conduction in all four cardiac chambers and its disruption in the presence of an abnormality or disease. In addition, atrial arrhythmias are typically asymptomatic and remain clinically undetected. In this study, our objective is to assess the clinical potential of a method pioneered in our laboratory, i.e., Electromechanical Wave Imaging (EWI) that combines the information from both the electrical (ECG) and mechanical (echocardiography) cardiac function into a single imaging modality that can simultaneously map, at very high frame rates, both the electrical and mechanical cardiac function in all four cardiac chambers, at both the presence and absence of disease. EWI is a unique technique that can noninvasively map the mechanical wave propagation as induced by the electrical activation of the heart, also known as the electromechanical wave. The multi-disciplinary team assembled encompasses all critical specialty areas such as ultrasound transducer design, ultrasound signal processing, conduction mapping hardware, cardiac electrophysiology in animals and humans and clinical diagnosis and treatment of arrhythmias. We propose the following specific aims: 1) design and implement novel systems that can provide optimized EWI imaging of atrial arrhythmias; 2) evaluate the performance of detection of atrial arrhythmias in canines in vivo; and 3) assess the treatment planning and guidance capabilities of radio-frequency (RF) ablation procedures of patients with atrial arrhythmias. This study could have a broad impact since the same imaging modality can easily be integrated into any commercial echocardiography system for immediate translation to the clinic. Furthermore, it can also be applied safely and noninvasively in conjunction with any diagnostic method, such as electrocardiography and echocardiography or, monitoring of therapeutic techniques.